The present invention is an improved method for hydrolyzing chlorosilanes having at least three chlorine atoms bonded to each silicon atom to form silicone resins. The method comprises adding at least one of hydridochlorosilane, tetrachlorosilane, or organochlorosilane to a two-phase mixture comprising a non-polar organic solvent, an aqueous phase comprising 0 to about 43 weight percent hydrochloric acid, and a surface active compound selected from the group consisting of selected organosulfates and alkali metal salts thereof. It is well known in the prior art that halosilanes readily hydrolyze in the presence of water to form silanols which condense to form polysiloxanes. Furthermore, it is well known that these two processes occur almost simultaneously when the halosilane contains three or more halogen atoms. The result of this rapid hydrolysis and condensation is an insoluble gel which is of little practical value. See, for example, Boldebuck, U.S. Pat. No. 2,901,460.
Numerous solutions to the above problem have been suggested. Boldebuck, supra, described for instance utilizing a hydrolysis medium comprising tetrahydrofuran and water to alleviate the gelling. Frye et al., U.S. Pat. No. 3,615,272, describe a process for forming hydrogensilsesquioxane resin comprising reacting a silane in a hydrocarbon solvent with sulfuric acid and an aromatic hydrocarbon, washing the reaction mixture with water and sulfuric acid until neutral, and recovering the product by evaporation of the solvent.
Bank et al., U.S. Pat. No. 5,010,159, teach a method of hydrolyzing hydridosilanes with 2 or more hydrolyzable groups which comprises forming an arylsulfonic acid hydrate containing reaction medium, adding the silane to the reaction medium, facilitating hydrolysis of the silane to form the polyester, and recovery of the polymer. It is taught that the arylsulfonic acid hydrate containing reaction medium can be formed either by dissolving an arylsulfonic acid hydrate in a solvent, such as an alcohol, or it can be generated by the preferred method of reacting an aromatic hydrocarbon with concentrated sulfuric acid.
Ezerets et al., SU (11) 1147723, teach a method of hydrolysis of methylchlorosilane alone or as a cohydrolysis with diorganodichlorosilanes or organotrichlorosilanes, with a functionality of 2.9 to 3 in a mixture of an aromatic hydrocarbon solvent and a water-miscible solvent. The method is characterized by the water-miscible solvent comprising acetic acid and concentrated hydrochloric acid and the presence of a water-soluble cationic surfactant. The water-soluble cationic surfactants are described as amine hydrochlorides, quaternary ammonium salts, and salts of protonated carboxylic acids, which contain 6 to 20 carbon atoms.
Hacker et al., WO 98/47941, describe a process for preparing hydridosiloxane and organohydridosiloxane resins. The process involves the steps of contacting a silane monomer with a phase transfer catalyst in the presence of a reaction mixture that includes a nonpolar solvent and a polar solvent. Hacker et al. state that the phase transfer catalysts are quaternary ammonium salts.
Shkolnik et al., SU (11) 1666469, describe a process for preparation of oligoorganohydridosiloxanes comprising conducting an acid hydrolysis of a mixture of phenyltrichlorosilane or vinyltrichlorosilane, dimethyldichlorosilane, and hexamethyldisiloxane in the presence of a sulfonated copolymer of divinylbenzene and styrene.
It is also known that nonionic surface active agents can effect the hydrolysis of diorganochlorosilanes. For example, Williams, U.S. Pat No. 4,412,080, teaches that cyclic dimethylpolysiloxanes can be prepared by hydrolysis of dimethyldichlorosilane and aqueous hydrochloric acid in the presence of a normal C6-16 alkyl sulfonic acid to give good yields of cyclic polysiloxanes.
The present invention is a process for producing silicone resins in high yield which are readily soluble in non-polar solvents. The method has the advantage of (1) not requiring the use of sulfuric acid, (2) not having the solvent be a reactant in the system as when the solvent is reacted with sulfuric acid to form an arylsulfonic acid hydride, thereby making the process easier to control, (3) having the hydrogen chloride generated by the hydrolysis of the chlorosilanes separate from the mixture as an anhydrous gas and thus is in a form in which it can be recycled to the method or otherwise used, and (4) allowing the aqueous layer containing the hydrochloric acid and the surface active agent to be directly recycled back into the method.
Resins prepared by the present method are unique in that for a given monomer distribution at a similar percent solids, they tend to favor a high degree of intramolecular cyclization relative to resins prepared by other procedures. Additionally, thin films of cured resins prepared by the present method can have high resistance to environmental induced stress cracking.
Polymers formed by the present method have excellent coating and sealing characteristics when cured to their ceramic or ceramic-like state. Such polymers have utility, for example, in coating electronic devices to form protective barriers.
The present invention is a method for hydrolyzing chlorosilanes having at least three chlorine atoms bonded to each silicon atom to form silicone resins The method comprises adding at least one of hydridotrichlorosilane, tetrachlorosilane, or organotrichlorosilane to a two-phase mixture comprising a non-polar organic solvent, an aqueous phase comprising about 0 to about 43 weight percent hydrochloric acid, and a surface active compound selected from the group consisting of organosulfates described by formula R2SO4H and alkali metal salts thereof, where R2 is selected from the group consisting of alkyl groups comprising about 4 to 16 carbon atoms and alkylphenyl groups comprising 7 to about 22 carbon atoms.
The present invention is a process for the preparation of a silicone resin. The process comprises adding at least one chlorosilane described by formula
R1xSiCl4-xxe2x80x83xe2x80x83(1)
to a two-phase mixture comprising a nonpolar organic solvent, an aqueous phase comprising 0 to about 43 weight percent hydrochloric acid, and a surface active compound selected from the group consisting of organosulfates described by formula R2SO4H and alkali metal salts thereof, where R1 is selected from the group consisting of hydrogen and monovalent hydrocarbon groups, R2 is selected from the group consisting of alkyl groups comprising about 4 to 16 carbon atoms and alkylphenyl groups comprising 7 to about 22 carbon atoms, and X=0 or 1.
The chlorosilane added to the present process can be a hydridotrichlorosilane, organotrichlorosilane, tetrachlorosilane, or a mixture thereof In formula (1), R1 can be hydrogen or a monovalent hydrocarbon group as exemplified by alkyls such as methyl, ethyl, propyl, octyl, dodecyl, and octadecyl; cycloalkyls such as cyclopentyl or cyclohexyl; cycloalkenyls such as cyclopentenyl or cyclohexenyl; aryls such as phenyl, tolyl, and naphthyl; alkenyls such as vinyl, allyl, and pentenyl; aralkyls such as benzyl and gamma tolylpropyl; and substituted hydrocarbon groups such as chloromethyl, 3,3,3-trifluoropropyl, and perfluoropropyl. Preferred is when R1 is selected from the group comprising hydrogen and hydrocarbon groups comprising 1 to about 20 carbon atoms. Preferred chlorosilanes for use in the present method are trichlorosilane, and methyltrichlorosilane.
The chlorosilanes described by formula (1) can be hydrolyzed alone or as a mixture of two or more and in addition may be co-hydrolyzed with diorganodichlorosilanes described by formula R12SiCl2 where R1 is as defined above.
The chlorosilanes are generally utilized in the form of a liquid. This liquid may consist essentially of the chlorosilane in its liquid state or it may comprise the chlorosilane mixed with a non-polar organic solvent to form a solution. If a solvent is used, the solvent can be any suitable non-polar hydrocarbon or water insoluble chlorocarbon which is a solvent for the chlorosilane. Exemplary of such solvents are saturated aliphatics such as dodecane, n-pentane, n-hexane, n-heptane and isooctane; aromatics such as benzene, toluene, and xylene; cycloaliphatics such as cyclohexane; halogenated aliphatics such as trichloroethylene, perchloroethylene and 3-chloropropane; and halogenated aromatics such as bromobenzene and chlorobenzene. Additionally, combinations of the above solvents may be used together as co-solvents for the chlorosilane. The preferred non-polar organic solvents are aromatic compounds and of these toluene is most preferred.
In the present process, to obtain good product yields it is preferred that the chlorosilane be diluted in a non-polar organic solvent, with toluene being a preferred solvent. Dilution of the chlorosilane in a non-polar organic solvent prior to addition in the process can provide for better dispersion of the chlorosilane in the two-phase mixture thereby reducing gel formation and improving yield. The chlorosilane may comprise about 10 to 80 weight percent of the chlorosilane and non-polar organic solvent mixture. Preferably the chlorosilane comprises about 20 to 60 weight percent of the chlorosilane and non-polar organic solvent mixture.
The chlorosilane may be added to the present process by any of those standard methods known in the art in processes for hydrolyzing such chlorosilanes. However, to maximize yields, it is preferred that the chlorosilane be added by a method which insures rapid dispersion of the chlorosilane into the two-phase mixture. Such methods can include adding the chlorosilane in a slow flow below the liquid mixture with vigorous stirring.
In a preferred process the chlorosilane in a non-polar organic solvent is added to a rapidly stirred two-phase mixture comprising a non-polar organic solvent, aqueous hydrochloric acid, and the surface active compound. By xe2x80x9ctwo-phasexe2x80x9d mixture it is meant a mixture comprising an organic phase and an aqueous phase. The non-polar organic solvent comprising one phase of the two-phase mixture can be any of those non-polar organic solvents as described above for diluting the chlorosilane and can be the same or different than any non-polar organic solvent used to dilute the chlorosilane prior to addition to the process. It is preferred that the non-polar organic solvent comprising a component of the two-phase mixture be the same as any solvent used to dilute the chlorosilane, with toluene being the preferred solvent.
The aqueous phase comprising 0 to about 43 weight percent hydrochloric acid comprising the second phase of the two-phase mixture should comprise at least a stoichiometric amount of water in relation to the silicon bonded chlorine atoms and preferably a stoichiometric excess. Generally an excess of water in the range of about 30 to 1000 mole percent is preferred, with an excess in the range 250 to 800 mole percent excess being most preferred. Generally the aqueous phase can comprise 0 to about 43 weight percent hydrochloric acid, with the aqueous phase comprising about 15 to 37 percent hydrochloric acid being preferred.
An advantage of the present process is that hydrogen chloride formed as a result of the hydrolysis reaction can be evolved as anhydrous hydrogen chloride gas when the aqueous phase is saturated with hydrogen chloride. Therefore it is preferred that the aqueous phase comprise at least about 35 Wt. % hydrogen chloride. The evolved hydrogen chloride may then be recovered as a gas and recycled to the process or used for other applications. The hydrogen chloride present in the aqueous phase may be added to the method separate as an aqueous solution or may be generated in situ by hydrolysis of the chlorosilane.
The present process requires the presence of a surface active compound selected from the group consisting of organosulfates described by formula R2SO4H and alkali metal salts thereof, where R2 is selected from the group consisting of alkyl groups comprising about 4 to 16 carbon atoms and alkylphenyl groups comprising 7 to about 22 carbon atoms. Preferred is when the alkyl groups represented by R2 comprise about 6 to 12 carbon atoms and the alkylaryl groups represented by R2 comprise about 9 to 18 carbon atoms. The surface active compound can be, for example, allyl sulfates having the formula CnH(2n+1)SO4H, where n equals about 4 to 16. The allyl sulfate may be, for example, C4H9SO4H, C6H13SO4H, C8H17SO4H, C10H21SO4H, C12H21SO4H, and C16H33SO4H. The surface active compound may be the corresponding metal salts of the alkyl sulfates where the alkali metal may be, for example, potassium or sodium. The alkali metal salt of the alkyl sulfate may be, for example, C6H11SO4xe2x88x92Na+, C8H17SO4xe2x88x92Na+, C10H21SO4xe2x88x92Na+, C12H25SO4xe2x88x92Na+, C16H33SO4xe2x88x92Na+, C8H17SO4xe2x88x92K+. The surface active compound can be an alkylphenyl sulfate described by formula CnH(2n+1)xe2x80x94C6H4xe2x80x94SO4H, where n equals 7 to about 22 carbon atoms, and the corresponding alkali metal salts thereof The alkylphenyl sulfate can be for example methyphenyl sulfate, propylphenyl sulfate, and the corresponding sodium and potassium salts thereof.
The concentration of the surface active compound in the aqueous phase of the two-phase mixture may be within a range of about 0.1 to 60 weight percent, based upon the weight of the water added to the process. Generally, it is preferred that the concentration of surface active compound comprise about 0.5 to 10 weight percent of the water added to the process. Typically, even more preferred is when the concentration of the surface active compound comprises about 0.5 to 2 weight percent of the water added to the process.
The temperature at which the present process can be conducted is not limiting and can generally be within a range of about 0xc2x0 C. to 100xc2x0 C., with a temperature within a range of about 10xc2x0 C. to 30xc2x0 C. being preferred.
In the present process, if desired, residual hydroxyl groups on the silicon atoms of the resin may be reacted with an organosilyl end-capper such as described by formula R3SiCl where R is monovalent hydrocarbon group as previously described. Preferred is when the end-capper is a trialkylchlorosilane. Even more preferred is when the end-capper is trimethylchlorosilane.
After the hydrolysis reaction of the present process is completed and the silicone resin formed, the two-phase mixture can be phase separated by a method such as settling. This process may, for example, be accomplished by merely ceasing agitation of the hydrolysis mixture and allowing it to spontaneously separate into immiscible layers in the reaction vessel. The layers that form comprise an organic layer which contains the silicone resin and the solvent, and an aqueous layer containing hydrogen chloride and the surface active compound.
Either before, during, or after this separation, it may be desirable to allow the organic layer to set for a period of time to provide for further condensation of residual silicon bonded hydroxyl and chlorine atoms present on silicon atoms of the silicone resin, thus causing increased structuring and/or increase in molecular weight of the silicone resin. Typically it is preferred that this bodying process be allowed to occur before separation of the two phase, if bodying is to be allowed to occur. To provide for stability of the silicone resin produced by the present method a wash process with or without neutralization may be useful. If the organic layer is to be washed water alone may be used, but it is preferred that the wash solution be an aqueous sulfuric acid solution. Wash solutions containing greater than about 5 Wt. % sulfuric acid are generally useful. The organic layer, either washed or unwashed, can be contacted with a neutralizing agent preferably in the presence of water which promotes hydrolysis of remaining chlorine atoms. The neutralizing agent should be sufficiently basic to neutralize any remaining acid species such as sulfuric acid, hydrogen chloride, and organic acids without significant catalytic rearrangement of the silicone resin or reaction of silicon bonded hydrogen with water. Suitable bases can include, for example, calcium carbonate, sodium carbonate, sodium bicarbonate, ammonium carbonate, ammonia, calcium oxide, and calcium hydroxide. It is generally preferred that the neutralizing agent be in the form of a solid, since this facilitates easy separation of the neutralizing agent from the organic phase. It is also generally preferred that the organic phase after washing and/or neutralization be dried and if necessary filtered to remove any water insoluble salts or other insoluble particulates which may effect the silicone resin properties. Any suitable drying agent such as magnesium sulfate, sodium sulfate, or molecular sieves may be used. In addition, the water may be removed by azeotropic distillation.
The silicone resin formed by the present process may be retained as a solution in the reaction solvent or if desired a simple solvent exchange may be performed by adding a secondary solvent and distilling off the first. Alternatively, the solid form of the silicone resin may be recovered by removing the solvent by a standard process such as azeotropic distillation.
The silicone resins that can be made by the present process are variable depending on the chlorosilanes used. The following non-limiting list of possible hydrolysates and co-hydrolysates, however, are specifically contemplated: fully condensed and near fully condensed resins including: (HSiO3/2)m, (R1SiO3/2)m, (HSiO3/2)s(R1SiO3/2)t, (HSiO3/2)s(R12SiO)t, and (R1SiO3/2)s(R12SiO)t; corresponding partially condensed resins which contain silanol described by formulas (HSiO3/2)s(H(HO)SiO)t; (R1SiO3/2)s(R1(HO)SiO)t, (HSiO3/2)w(H(HO)SiO)s(R1SiO3/2)t(R1(HO)SiO)z, (HSiO3/2)w(H(HO)SiO)s(R12SiO)t(R12(HO)SiO1/2)z, (R1SiO3/2)w(R1(HO)SiO)s(R12SiO)t(R12(HO)SiO1/2)z, (R13SiO1/2)s(SiO2)t((HO)SiO3/2)z; and corresponding triorganosilyl endcapped resins described by formulas (R13SiO1/2)s(HSiO3/2)t, (R13SiO1/2)s(R1SiO3/2)t, (R13SiO1/2)(HSiO3/2)t(R1SiO3/2)z, (R13SiO1/2)s(HSiO3/2)t(R12SiO)z, R13SiO1/2) s(R1SiO3/2)t(R12SiO)z, (R13SiO1/2)s(SiO2)t, (R13SiO1/2)w(HSiO3/2)s(R12SiO)t(SiO2)z, and (R13SiO1/2)w(R1SiO3/2)s(R12SiO)t(SiO2)z, where R1 is as previously described and each R1 can be the same or different, m is 8 or greater and the mole fractions of w, s, t, and z in the above copolymer silicone resins total 1.